This invention relates generally to x-ray methods and apparatus, and more particularly to methods and apparatus that provide gating single- and multiple-exposure digital x-ray applications.
X-ray has traditionally been a single exposure modality resulting in a projection image of the anatomy being examined. With the introduction of rapid-readout digital detectors, advanced applications utilizing multiple exposures have been enabled. These advanced applications result in multiple images, which provide additional information to the radiologists to aid in diagnosis.
Dual-energy subtraction imaging has been proposed and investigated by many researchers as a means of reducing the impact of overlying, superimposed anatomic structure on disease detection in chest radiography. Dual-energy is an example of an application where two exposures are acquired in rapid succession, it involves taking two exposures of the patient using different energy x-ray beams. By exploiting the differences in the energy dependence of attenuation between bone and soft tissue, the contrast of the bone can be eliminated producing a soft-tissue only image, or the contrast of the soft tissue can be reduced to produce a bone image. Energy subtraction computed radiography (CR) systems have been developed but are hampered by poor subtraction effectiveness, workflow inconveniences, and the inherent detection inefficiencies of the CR technology. Despite these limitations, CR based dual energy has been shown to increase the detection of lung cancer.
A digital flat-panel imaging system based on a CsI:TI scintillator coupled to an amorphous silicon TFT array has been developed. For radiographic applications, the panel has a size of 41 cm×41 cm, 2048×2048×200 mm pitch. The key enabler for dual-exposure dual-energy imaging is the ability to rapidly read the image data off the commercially available detector. This technology has evolved to the point where these techniques are receiving widespread clinical acceptance and improving the detection of thoracic pathology, and the application of this technique is now being applied to non-thoracic imaging tasks. Improved detection of calcified structures and anecdotal reports of the detection of coronary calcifications have been reported. The clinical significance of these observations is only beginning to be investigated.
Tomosynthesis is another application where several rapid exposures are acquired in rapid succession as the source traverses an angular range relative to the detector. These exposures are used to reconstruct thin image planes through the anatomy being examined. This process removes under- and over-lying structures for a given reconstructed image plane.
With the current dual-energy and tomosynthesis systems, exposures can be acquired with less than a 200 msec interval between acquisitions. Although this interval is relatively short, motion of tissues in this interval can lead to the creation of artifacts in the final subtracted or reconstructed images as shown in one of the Figures for the example of dual-energy imaging. Therefore, we have developed a prototype dual-energy gating system that has been validated on anthropomorphic phantoms.
Currently, with single-exposure or multiple-exposure x-ray imaging, the patient is usually asked to hold their breath. However, there is no mechanism to ensure this, particularly in patients whose health is compromised. Further, since the heart is beating during the procedure, there is no mechanism to ensure that all acquisitions happen at a known point in the cardiac cycle. It is hypothesized that cardiac motion is primarily responsible for observed motion artifacts in thoracic dual-energy imaging, and both cardiac and respiratory motion can cause artifacts during the longer total duration of a tomosynthesis acquisition series.
This is important for two principle reasons:
a) When information from different acquisitions is combined to create an image, if the acquisitions are not exactly aligned, the resulting image will have “mis-registration” artifacts. These artifacts may be aesthetically unpleasing and artifact reduction has always been a goal for all diagnostic imaging (DI) modalities.
b) If quantitative metrics such as size measurements are to be calculated, knowledge of the exact acquisition time with respect to respiratory and cardiac cycles is useful in addition to other system-related information such as distance from source, detector, etc.
Therefore, below are designs and workflows for gating single- and multiple-exposure digital X-ray applications.